This invention relates to a unique method of bonding a fabric cover to a substrate base for an interior trim panel such as a vehicle headliner.
In the prior art, headliners are often manufactured from a fabric cover layer which is bonded to an underlying base. The base provides shape and rigidity to the cover. In one very successful type of vehicle headliner, the base is provided by several paper layers. In particular, a fluted paper, which is similar to the corrugated paper utilized for cardboard, is used as a core. Kraft paper is laminated on both the top and bottom of the fluted paper. In essence, this results in a similar to standard cardboard.
In the prior art, the kraft paper layers have been adhered to the fluted paper layer by polyethylene film adhesive layers. Thus, it is known to provide a sandwich of outer kraft paper layers, and an inner fluted paper layer with intermediate polyethylene film adhesive layers. The several layers are then heated, and the kraft paper adheres to the central fluted layer.
Two standard methods are then utilized to adhere the cover to this substrate base. In one method, the tool which is utilized to heat the layers to form the substrate, is also utilized to heat and activate another polyethylene adhesive layer placed on the base substrate. An outer cover layer is placed outwardly of this adhesive layer. The adhesive layer is heated such that it then bonds the cover to the substrate. In this prior art method, the tool utilized to form the headliner into its desired shape and to secure all of the layers together, uses a forming tool having heated top and bottom halves. With this method, there has sometimes been difficulty maintaining the dimensional integrity of the substrate, particularly during the subsequent heating to adhere the cloth layer. This is believed due to the repeated heating of the substrate.
In a second method, a second tool is utilized to adhere the outer cover layer. The substrate base is formed in a forming tool, with a heated top and bottom half. The substrate base is then removed from the forming tool and placed into a bonding tool. The bonding tool receives the substrate base, a layer of polyethylene adhesive, and the outer cover. The bonding tool then closes on the several layers. The latent heat in the base layer alone is relied upon to actuate the polyethylene adhesive layer. While this method does provide improvements in the final dimensional integrity of the overall headliner, it requires undesirably large amounts of time to actuate the adhesive layer.
It is a goal of vehicle headliner assembly lines to manufacture as many headliners in as small a time period as is reasonably possible.